The present invention relates generally to ultrasonic testing and inspection of welding seams, and, more particularly, to a system for performing automated ultrasonic testing and inspection of the welds of railroad tank cars.
Federal regulations (HM-201) directed to the testing of welds in railroad tank cars were promulgated by the Department of Transportation (DOT) in 1995. More specifically, HM-201 guidelines prohibit the use of hydrostatic tank testing and, instead, require that welds in high-stress areas be tested for structural integrity using an approved non-destructive testing technique. The DOT has identified the circumferential girth butt-welds in the bottom portion of the tank shells of railroad tank cars as high-stress areas. As a result, these welds must be tested and inspected for subsurface flaws or defects via an approved non-destructive testing technique. Ultrasonic flaw detection is one of the approved non-destructive testing techniques.
Ultrasonic flaw detection or testing typically utilizes a probe or transducer that passes in close proximity along the front surface of the weld being tested. The transducer communicates with the weld via a coupling fluid such as water or gel. The probe imparts high-frequency sound waves into the weld through the fluid. The sound waves are reflected back to the probe from the back surface of the weld or internal flaws. Monitoring of this reflection of the sound waves is used to determine weld characteristics such as thickness and the presence of defects or flaws in the form of discontinuities.
Automated ultrasonic flaw detection systems, whereby motion is induced between the weld being tested and one or more probes, have been in use for over 35 years in industries such as the welded tube industry (i.e. pipelines, structural steel, etc.). Patents illustrating this technology include U.S. Pat. No. 5,585,565 to Glascock et al.; U.S. Pat. No. 5,174,155 to Sugimoto; U.S. Pat. No. 4,627,289 to Fukuda et al.; U.S. Pat. No. 4,375,165 to de Sterke and U.S. Pat. No. 4,305,297 to Ries et al. All of these patents, however, illustrate automated ultrasonic testing systems that operate on the exterior surface of the pipe being tested. When ultrasonic testing is used, the welds of railroad tank cars must be scanned from inside, that is, on the interior surface, of the tank.
In the past, ultrasonic testing of railroad tank cars has been performed manually by technicians utilizing hand-held transducers or probes. Such ultrasonic testing of the tank car welds requires that the technician use multiple scanning patterns by which the proximity and angle of the probe, with respect to the weld, is varied. As a result, manual scanning is expensive and time consuming. Companies are motivated to minimize the cost of tank car testing for obvious reasons. Furthermore, in order to maximize utilization and therefore profits, companies desire that their tank cars be returned to service as quickly as possible. As such, it is desirable to provide an ultrasonic testing system for tank cars that operates quickly.
In addition, the accuracy of the results obtained in manual ultrasonic testing depends a great deal upon the skill of the technician. As such, it may be difficult to obtain consistent and reliable test results. In other words, two technicians may obtain different results even though they scanned the same weld. It is therefore desirable to provide an ultrasonic testing system that consistently provides effective performance.
Accordingly, it is an object of the present invention to provide an ultrasonic testing system for tank car welds that is automated.
It is another object of the present invention to provide an ultrasonic testing system for tank cars that will test the circumferential girth butt-welds in the bottom portion of the tank car shells.
It is another object of the present invention to provide an ultrasonic testing system for tank cars that is inexpensive and operates quickly.
It is still another object of the present invention to provide an ultrasonic testing system for tank cars that consistently provides effective performance and reliable test results.
The present invention is directed to an ultrasonic testing system for inspecting the circumferential girth welds of a railroad tank car for internal or surface flaws or defects. The system includes a probe trolley to which six probes are mounted. The probe trolley is clamped to a drive unit that travels upon a track that is positioned on a surface adjacent to the weld being inspected. The track is attached to the inner surface of the tank in a removable fashion by magnetic mounts and is oriented to run parallel to the weld.
The probe trolley includes a top plate to which each of the probes is mounted via a probe mounting assembly. Each probe mounting assembly includes a bearing holder secured to the top plate with a bearing disposed therein. A piston is slidably received in the bearing and is connected to a probe shoe that holds the probe in a removable fashion. The probe is attached to a wedge prior to insertion into the probe shoe. The wedge holds the probe at the appropriate angle with regard to the thickness of the weld and the surface adjacent to the weld.
The probe shoes are mounted to the pistons by swivel balls and compression springs are utilized between the probes shoes and the bearing holders. Furthermore, coupling fluid is supplied to the probe shoes so that a layer of coupling fluid exists between the probes and the surface adjacent to the weld. As a result, the probe shoes float upon a layer of coupling fluid and ultrasonic beams emitted by the probes pass through the coupling fluid and into the tank wall and weld and are reflected therefrom.
A computer communicates with the probes so that data from the probes may be collected, analyzed, displayed and stored. By rotating the probe trolley 180xc2x0 and performing a second scan or pass, the weld is effectively subjected to scanning by twelve probe positions or scanning patterns.
The following detailed description of embodiments of the invention, taken in conjunction with the appended claims and accompanying drawings, provide a more complete understanding of the nature and scope of the invention.